In my Honest opinion the droplets of water hitting the ground when it rains make the rain effect it's self look blah and fake. I think you could loose the splash effect from the rain and it would look much better and do more performance wise for lower end pc' users. This is just a thought on my end.
I run a high end PC my self with 8 gigs ram 64 bit with all trimmings so I'm not asking to dumb this game down cause I have issues lol. Not with my rig just think it makes the game look off when it rains when it falls on ground it don't look bad but if watch it drop on water it looks Atari in a way to me. An it inter-fears with the waters look when the water is reacting to it in its own effect. It's a very nice effect but in order to appreciate the effect you have to move the screen in 3rd person view so you can see the ground just right to actually with the necked eye and catch the nice work that went in to that effect. As far as normal running game play no one will really pay any attention to it being there maybe at first ah thats cool but then its forgotten.